So you start a build, and about halfway through your extruder stops pushing filament. The pulley turns but the idler just sits there.

Great. The bolt is loose again. Another agonizing ritual of pulling apart the extruder and trying to tighten (but not break!) the bolt. JOY.

Not so fast!

I've discovered (through many painful minutes of trying to squeeze filament by hand) that skeinforge can insert m-codes for changing the temperature in your build. And if those changes drop the working temperature enough, the plastic can harden, and the motor will strip the plastic at the point where it's touching, eventually making it impossible to extrude.

To test for this one, bring the bot up to temperature and send an extrude command. If you've stripped the filament, nothing will happen at first, but if you force the plastic past the stripped spot, the extruder will start to extrude on its own again!

Search your gcode for temperature changes, and if anything's lower than it should be, alter it (or your skeinforge settings!)